Transparent conductive films in which a transparent electrode layer formed of a conductive oxide such as indium-tin composite oxide (ITO) is formed on a transparent film substrate are widely used for touch panel position detection etc. For improvement of transparency, reduction of resistance, suppression of a change in resistance value, and so on, crystallized conductive oxides are used in transparent electrodes.
Generally, a roll-to-roll sputtering apparatus is used for production of a transparent conductive film. In production of a transparent conductive film, it is necessary to deposit a transparent electrode layer to the extent that the film has heat resistance. Accordingly, the deposition temperature (substrate temperature) is generally 200° C. or lower, and the transparent electrode layer immediately after the deposition by roll-to-roll sputtering is an amorphous film. The amorphous transparent electrode layer is crystallized when heated under an oxygen atmosphere.
It is known that in production of a transparent conductive film by roll-to-roll sputtering, an outgas from a substrate film during sputtering deposition influences the film quality and crystallization behavior of a transparent electrode layer. For example, Patent Document 1 discloses that when a first thin-film is deposited with a low power density, and a film is then deposited thereon at a high rate with a high power density, damage to a substrate film can be minimized, and generation of an outgas from the substrate can be suppressed. Patent Document 2 discloses that when a film substrate is heated before deposition, or a dielectric layer of silicon oxide or the like is provided on a film substrate, the amount of an outgas resulting from plasma damage etc. during sputtering deposition can be reduced to control the crystallinity of a transparent electrode layer.
Patent Document 3 discloses that uniformity of crystal grain size in the transparent electrode layer is enhanced when a cleaning (bombardment) of the surface of a film substrate is performed before deposition of a transparent electrode layer by generating plasma in the presence of an inert gas such as an argon gas. Specifically, organic components are volatilized from the film substrate by bombardment, and therefore the partial pressure of a gas with a mass number of 28 in an atmosphere during deposition of the transparent electrode layer is reduced, so that crystal grains in the transparent electrode layer can be made uniform.
Patent Document 4 discloses that when a transparent electrode layer has a stacked configuration of two or more layers, both reduction of the resistance of the transparent electrode layer and short-time crystallization of the transparent electrode layer can be achieved. Specifically, an ITO layer having a low tin oxide content is provided on the transparent conductive film surface side (side away from the film substrate) to accelerate formation of crystal nuclei, and an ITO layer having a high tin oxide content is provided on the film substrate side to increase carriers, so that short-time crystallization and reduction of the resistance can be achieved. Further, Patent Document 4 describes that it is preferable to evacuate the inside of a sputtering apparatus to a water partial pressure of 1×10−4 Pa or less before the start of deposition, so that deposition is performed in an atmosphere cleared of impurities such as an outgas from the film substrate.
Patent Document 5 discloses that when a dielectric layer of silicon oxide or the like is provided on a substrate film, a transparent electrode layer is sputtering-deposited thereon at a low oxygen partial pressure, the transparent electrode layer can be crystallized even by low-temperature and short-time heating (or at room temperature). Patent Document 5 describes an estimation principle in which low-temperature and short-time crystallization can be performed by increasing oxygen deficiency in the conductive oxide. Patent Document 5 also describes that the dielectric layer of silicon oxide or the like acts as an underlying layer for film growth, and also acts as a gas barrier layer which reduces plasma damage to the substrate film during deposition of the transparent electrode layer, so that an oxygen gas generated from the substrate is inhibited from being captured in the film, leading to an increase in oxygen deficiency in the film, and thus crystallization can be performed at a low temperature in a short time.